1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a chemical mechanical polishing method for manufacturing a semiconductor device.
2. Description of the Related Art
Recently, with the increased degree of integration of semiconductor devices and introduction of various materials, the importance of planarization processes has increased. Among such processes, mechanical polishing results in the formation of deformed layers, causing product defects, while chemical polishing does not cause the formation of such deformed layers, it has a limitation in that precise flatness cannot be achieved. As such, chemical mechanical polishing (CMP) is primarily employed which has the advantages of both chemical and mechanical polishing methods.
In such a chemical mechanical polishing method, a wafer having a polishing-target film is polished by a pad and slurry. A polishing table, to which the pad is attached, is rotated, while a head part of the polishing table simultaneously rotates and fluctuates and applies given pressure to a wafer. The wafer is mounted on the head part of the polishing table by surface tension or a vacuum. Self-load of the head part and pressure applied thereto results in contact between the pad and wafer surface, and slurry flows through minute interstices defined between interfaces thereof, i.e., pores of the pad. Consequently, mechanical removing action is effected by slurry-constituting polishing particles and surface protrusions of the pad and at the same time, chemical removal is also affected by chemical components in the slurry.
Upon performing a planarization process via use of chemical mechanical polishing, a removal rate, which refers to the ratio of film material to be removed, is unfortunately non-uniform depending upon changes in the position of wafer. For example, when the wafer is planarized by removing a polysilicon film to a predetermined thickness or the planarization process of the wafer is performed until the film materials beneath the polysilicon film are exposed, the removal rate of polysilicon film varies depending upon the position of wafer. As a result, over-polishing beyond a conventional removal amount is caused and thereby a great deal of problems may occur in subsequent processes.
FIG. 1 is a view illustrating distribution of a removal amount of a polishing-target film with respect to the position of a wafer, in a general chemical mechanical polishing method.
As shown in FIG. 1, when comparing respective removal amounts at a central part and edge of a wafer 100 after a chemical mechanical polishing process was carried out on the polysilicon film, it can be seen that the removal rate at the edge of the wafer 100 is higher than at the central part of the wafer 100. That is, the rate at which the polysilicon film is removed at the edge of the wafer 100 is higher than the rate at which the polysilicon film is removed at the central part of the wafer 100. Consequently, over-polishing occurs at the edge of the wafer 100, or insufficient polishing is put into effect at the central part of the wafer 100.
FIG. 2 is a view showing state distribution of chips in a wafer to which a conventional chemical mechanical polishing method is applied.
As shown in FIG. 2, according to an image obtained from examination of the wafer to which the conventional chemical mechanical polishing method was applied, a central part of a wafer 200 is bright, while the edge of the wafer 200 is dark. These results denote a high probability of occurrence of defective chips at the edge of the wafer 200. One of causes responsible for the occurrence of such defective chips is non-uniformity of the target film removal rate in a chemical mechanical polishing process. As such, it is readily seen that the total yield of products may be reduced due to the non-uniform removal rate exhibited by the conventional chemical mechanical polishing method.